Laser diodes are known in the form of so-called laser bars having an active radiation-generating layer that is subdivided into a plurality of parallel, strip-type emission zones transversely arranged with respect to the emission direction. See for example, EP 0 064 339 A1. Laser diodes of this type are usually contacted by means of two contact areas extending laterally over all the emission zones, so that the individual strip-type emission zones are electrically connected in parallel. By virtue of the parallel arrangement of the emission zones, it is possible to achieve a particularly high optical power in comparison with a laser diode having a single emission zone, with the result that laser bars of this type are suitable in particular for high-power applications.
Cooling is accorded particular importance in the case of high-power laser diodes. Without adequate cooling, the resulting heat loss would lead to a major rise in temperature, so that the semiconductor body would be thermally overloaded and consequently destroyed within a very short time. For cooling purposes, the semiconductor body of the laser diode may be mounted for example onto a metal plate with sufficient thermal capacity and thermal conductivity.
In order to achieve even higher optical powers, such laser bars with respective cooling elements can be stacked vertically one above the other. However, such a device requires a comparatively high outlay on materials and production complexity since each semiconductor body is, first of all, mounted onto the respective cooling element and then the cooling element together with the semiconductor body fixed thereon are stacked one above the other. Each of these mounting steps has to be performed with high precision in order to ensure that all emission zones are aligned exactly with one another. Furthermore, the emission zones are at a comparatively large vertical distance from one another because of the cooling elements situated in between, said distance making it more difficult to focus the generated radiation onto a common center. However, particularly for pump applications with high powers, it is essential that the generated radiation can be focused as well as possible.